Cement systems, such as Portland cement, typically are subject to shrinkage during and after setting and hardening. In some applications such shrinkage is problematic. For example, in downhole applications for cementing a casing in a well and for abandonment plugs in wells, it is crucial that good bonding occurs between the set cement and the casing and/or between the set cement and the formation borehole wall in order to achieve effective zonal isolation. Poor cement/formation bonding, poor cement/casing bonding, expansion and contraction of the casing resulting from internal pressure or thermal stress, and inadequate mud removal all contribute to the formation of small gaps or “microannuli” at the cement/casing or cement/formation interface. These microannuli allow communication between the zones through which the wellbore extends.
Cement systems that expand slightly after setting are a proven means of preventing and/or sealing microannuli and improving primary cementing results. The improved bonding is the result of mechanical resistance or tightening of the cement against the casing and formation. In unrestrained environments, such as cement use in buildings and roads, expansion of the cement during setting and hardening can result in cracking and failure. In the restrained downhole environment, the cement expands to eliminate void spaces and reduce internal cement porosity.
Current additive compositions that are introduced into Portland cements to provide expansive cement typically rely on elevated temperatures to achieve a sufficient expansion effect, often above 100° F. (37.8° C.). There is a need, however, for expansive Portland cement systems that achieve sufficient expansion at temperatures below 100° F. (37.8° C.) and more typically at temperatures below room temperature (about 73° F. or about 23° C.).